Studies are designed to elucidate the role of bone membranes in regulating the fluxes (of Ca ions and Pi, in particular) into and out of the skeleton. It is planned to develop microelectrodes for the measurements of pH and/or electromotive force generated by periosteal and endosteal membranes of embryonic frontal bones. Chamber studies will be made to quantitate ion fluxes across the membranes of membranous bones. The potassium content of bones will be examined in animals subjected to a variety of homeostatic stresses with respect to Ca ions metabolism. BIBLIOGRAPHIC REFERENCES: Neuman, W.F., M.W. Neuman, P.J. Sammon and K. Lane: The metabolism of labeled parathyroid hormone. II. Methodological Studies. Calc. Tiss. Res. 18, 241-250 (1975). Neuman, W.F., M.W. Neuman, P.J. Sammon and K. Lane: The metabolism of labeled parathyroid hormone. III. Studies in rats. Calc. Tiss. Res. 18, 251-261 (1975).